zipper -package:zippers

Create a zipper, focused on the top-left value.
Not on Stackage, so not searched. Generic zipper for families of recursive datatypes
A zipper is a structure for walking a value and manipulating it in constant time. This module was inspired by the paper: Michael D. Adams. Scrap Your Zippers: A Generic Zipper for Heterogeneous Types, Workshop on Generic Programming 2010.
Zipper structure, whose root type is the first type argument, and whose focus type is the second type argument.
This module provides a two-dimensional text zipper data structure. This structure represents a body of text and an editing cursor which can be moved throughout the text, along with a set of editing transformations. Text zippers are generalized over the set of data types that might be used to store lists of characters (e.g., String, Text, etc.). As a result, the most general way to create a text zipper is to use mkZipper and provide all of the functions required to manipulate the underlying text data. Implementations using Text and String are provided.
Creation date: Thu Jul 23 08:42:37 2020.
This is an infinite bidirectional zipper
Based on «Scrap Your Zippers: A Generic Zipper for Heterogeneous Types. Michael D. Adams. WGP '10: Proceedings of the 2010 ACM SIGPLAN workshop on Generic programming, 2010» ( Compared to the original syz package, this implementation (based on GTraversable) gives more flexibility as to where a zipper may point to and what is considered as siblings. Specifically, a zipper may point to any element which gtraverse applies its function to.



Consider the classical example: lists. With syz, a list is interpreted as a right-balanced tree.
>>> let z = fromJust . down' $ toZipper ['a'..'d']

>>> getHole z :: Maybe Char
Just 'a'
The zipper z points to the first element of the list. Now let's move to the right:
>>> let z' = fromJust . right $ z

>>> getHole z' :: Maybe Char

>>> getHole z' :: Maybe [Char]
Just "bcd"
Instead of pointing to the second element of the list, as one might expect, the zipper z' points to the tail of the list. In order to actually move to the second element, we need another down':
>>> let z'' = fromJust . down' $ z'

>>> getHole z'' :: Maybe Char
Just 'b'


GTraversable-based zippers behave more intuitively in this regard, thanks to the uniform instance for lists.
>>> let z = fromJust . down' $ toZipper ['a'..'d'] :: Zipper Typeable [Char]

>>> getHole z :: Maybe Char
Just 'a'
So far it's more or less the same as with syz. We needed to add a type annotation for the zipper itself to clarify the context which should be available at each hole (Typeable in this case). Now let's see what's to the right of us:
>>> let z' = fromJust . right $ z

>>> getHole z' :: Maybe Char
Just 'b'
That is, we jumped right to the second element of the list. Likewise,
>>> let z'' = rightmost z

>>> getHole z'' :: Maybe Char
Just 'd'
So, unlike in syz, all of the list elements are siblings.
A generic zipper with a root object of type root.
Create a zipper with a different focus type from the outer type. Will return Nothing if there are no instances of the focus type within the original value.
Zipper utils that weren't in Control.Comonad.Store.Zipper Adds some utility functions for and reexports Control.Comonad.Store.Zipper